With conventional carbon electrodes (including also graphite electrodes) a pair of longitudinally extending electrode sections are coupled by means of a threaded carbon (or graphite) nipple which is threaded into correspondingly threaded opposed sockets of the electrode sections, with the result that the respective opposing butt faces of the electrode sections are brought into abutting contact. As an electrode section is consumed in the course of furnace operation, a new electrode section is tandemly coupled in the same manner so that furnace operation can proceed continuously. That is, the lower end of the column is consumed in the furnace, the entire column is lowered to maintain the operation. Electrode sections are joined to the top of the column to replenish the consumed columns. However, there is occasional mechanical failure, i.e. breakage of a threaded nipple joint which requires the interruption of electric furnace operation.
U.S. Pat. No. 4,152,533 is directed to nipple joint breakage and addresses the problem of stresses at the first few bottom threads of an electrode socket, by chamfering these threads. U.S. Pat. No. 4,375,340 addresses the problem of stresses at or near the mid-length of a threaded nipple which are relieved to increase the strength of the joint. These prior art techniques do not, however, eliminate joint failures due to electrode nipple misalignment and this has remained a serious industrial concern.